1. Field of the Invention
The present invention relates to a fiber with a ferrule used for an optical communication, an optical module using the fiber, and a method for manufacturing the optical module. More particularly, this invention relates to an optical module which can prevent a molding resin from adhering on a top end portion of an outer surface of the ferrule.
2. Description of the Related Art
To reduce the size and cost of an optical transmitter/receiver, it is required to mount a semiconductor laser (LD) and a monitor photodiode (M-PD) on a substrate such as a Si bench by the surface mounting technique. FIGS. 6 and 7 show a manufacturing process of an optical module. FIG. 6 is a flowchart of the manufacturing process of the optical module, and FIG. 7 is an explanatory view of a manufacturing method of the optical module.
First of all, a Si bench 21 having a V-groove for fixing an optical fiber 14 and an electrode pattern for soldering a LD 22 and a M-PD 23 is prepared.
The LD 22 and the M-PD 23 are soldered onto the Si bench 21, and the optical fiber 14 inserted into a ferrule 11 is fixed to the Si bench 21 by the resin. An intermediate product in this state is called a sub-module. At fixing the optical fiber 14, the optical fiber 14 is sandwiched between a glass plate 40 and the Si bench 21.
The sub-module is fixed onto a die pad of a lead frame 20, wire bonded and sealed with a resin by the transfer molding technique, so as to form a resin molded portion 13.
Next, a tie bar 27 and a frame 28 of the lead frame 20 are cut, each lead 29 is electrically isolated. The lead 29 exposed from the resin molded portion 13 is bent at a predetermined angle.
In the above process, a state within a mold at the time of the transfer molding is illustrated in FIGS. 8A-8C. FIG. 8A shows a state where the sub-module fixed on the lead frame is accommodated within the mold before the resin is filled into the mold. In this state, the resin is filled into the mold 30 from a resin filler hole 32 formed at an end face of the mold 30, thereby sealing the sub-module fixed on the lead frame 20 as shown in FIG. 8B.
However, with the above technique, the resin is adhered on a portion of the ferrule 11 exposed from the resin molded portion 13, resulting in a problem of increasing the coupling loss as the connector, or increasing an inferior optical module to lower the yield.
That is, when the sub-module is accommodated within the mold, and transfer-molded, as shown in FIGS. 8A and 8B, the resin exudes (or leaks) from a small gap between the mold 30 and the ferrule 11. In extreme cases, an exuded (or leaked) resin 16 is adhered and covered around a top end side of the ferrule 11, as shown in FIG. 8C.
This cause is considered as below. At the time of transfer molding, the resin temperature is increased up to about 170° C., for example, to soften the resin, and in this state, the resin is injected through the resin filler hole under a high pressure of about several 10 kg/cm2 to about several 100 kg/cm2. The injected resin is filled in a space within the mold, and cured with the elapse of time. Here, the ferrule is made of hard ceramic, and hardly deformed when sandwiched between upper and lower mold parts of the mold. Therefore, a gap as large as several μm to several 10 μm is produced between the surface of ferrule and the mold. From this gap, uncured resin is exuded (or leaked) and then cured at the gap between the ferrule and the mold.
The ferrule has a diameter of 1.25 mm, for example. If there is even a slight irregularity of the resin on the outer surface of the ferrule, it impedes the proper fitting with an optical fiber connector of the other side, leading to the dispersed coupling power and the lower yield. Especially, if the resin is exuded remarkably at the time of molding, the optical fiber end face is covered with the resin, as shown in FIG. 8C, thereby increasing an inferior optical module to lower the yield and increase the cost.